The demand for ruminants such as cattle, sheep, etc. has increased considerably in recent years. The supply of feed for ruminants, however, has failed to keep pace with increased demand, and the cost of such feed has increased. It is important that improved means be found for the efficient use by ruminants, having a developed rumen function, of the nutrients present in normal feeds. New and more efficient growth promoters are continually being sougth to give ruminants increased weight gain (referred to as growth promotion) and increased weight gain per pound of normal feed (referred to as increased feed efficiency or increased efficiency of feed utilization).
Various antibiotics have been suggested as growth promoters for various animals. See, for example, U.S. Pat. Nos. 3,790,668, 3,794,732 and 3,937,836. U.S. Pat. No. 3,914,428 suggests the use of 2-arylimino-1,3-dithietane compounds for this purpose.
It has also been proposed to improve efficiency of amino acid utilization by the use of certain amino acids as in U.S. Pat. No. 3,080,234, but there are limiting factors related to the proportions of certain amino acids in the plasma.
Certain lysine derivatives in which the carboxyl group is esterified and the 6-amino group bears certain substituents are disclosed as anti-allergic compounds in U.S. Pat. No. 3,539,602.
The use of the 2,2,2-trichloroethyl group for carboxyl protection during peptide synthesis is described in Can. J. Chem. 1973, 51(2), 208-14.
It has been found that the trichloroethyl esters of essential amino acids provide superior growth promoting properties and increase feed utilization efficiency when supplied in the feed of ruminants.
The chemical composition of the rumen fluid provides a means for ascertaining feed efficiency and the weight gain of the ruminant. Rumen fluid contains a substantial proportion of volatile carboxylic acids, including acetic, propionic and butyric acids. These acids, which provide the principal source of energy for the ruminant, are derived from carbohydrate fermentation by rumen microflora. Propionic acid is particularly indicative of feed efficiency and weight gain; i.e., increases in the level of propionic acid in rumen fluid are immediately reflected by improved feed utilization by the ruminant. Chemical changes in the rumen fluid can be measured by chemical analysis of samples of rumen fluid withdrawn from a ruminant.
Based on the knowledge of the foregoing, a practical method of testing growth promoters in vitro has been the simulation of conditions in the rumen with fermentation reactions. Such a method comprises adding the test substance to a substrate such as ground hay, corn or mixtures of feed materials. Rumen fluid from a fasted ruminant (bovine, ovine, or caprine) is mixed with a buffer solution and added to a fermentation flask containing the test additive and the substrate. The flask is purged of oxygen, stoppered with a pressure release valve, and incubated at 39.degree..+-.1.degree. C. for periods up to 48 hours. The change in volatile fatty acid concentration is determined by chemical analysis of the rumen fluid before and after fermentation. As a control, the above experiment is run without a test additive.
The correlation of rumen fluid analysis and growth stimulation is well established and can be corroborated by in vivo experiments which measure ruminant weight gain and feed efficiency over a period of time.